Watermarking media data (e.g. media files and/or media signals) generally involves embedding or otherwise adding information to the media data (i.e. “marking” the media data). In many applications, it is preferable that the information embedded in the media data does not substantially alter the human perception of playback of the media content. A watermark may generally comprise any information, such as, for example: encryption keys, authentication information, indications of ownership, indications of user ID or the like.
In the example of audio media data, watermarking processes typically exploit the human audio perception's inability to detect slight changes in the playback of audio content. When a watermark is embedded into audio data, it is generally desirable that when the audio data is played back, it is difficult for a human to perceive differences between playback of the watermarked audio content and playback of the original non-watermarked audio content.
It is generally desirable that, once embedded, a watermark be relatively robust to manipulation of the resultant watermarked media data. By way of non-limiting examples, it is desirable that the watermark be recoverable after: compression of the watermarked data; addition of noise to the watermarked data; D/A and A/D conversion of the watermarked data; resampling of the watermarked data; filtering of the watermarked data; changing the volume of the watermarked data; and/or other manipulation of the watermarked data.
It is also generally desirable that it be relatively difficult to filter or otherwise remove the watermarking from the watermarked media data without significantly degrading the playback quality of the media content.
Prior art watermarking techniques have yet to achieve some or all of the aforementioned desirable characteristics to a level sufficient to gain widespread commercial acceptance.